In the related art, various devices are suggested as a slide door device for a vehicle. As shown in FIG. 5, for example, in a slide door device for a vehicle disclosed in JP 2003-335136A (Reference 1), a body side lower rail 81 is installed along a lower edge of a door opening 80a which is formed on the side of a vehicle body 80, and a body side center rail 82 is installed in a rear quarter panel 80b of the door opening 80a. In addition, a body side guide roller unit 83 is connected to the rear upper side of the body side lower rail 81, and the body side guide roller unit 83 is connected to the front lower side of the body side center rail 82.
On the other hand, in a slide door 86, a door side guide roller unit 87 which can slide on the body side lower rail 81 is connected to the front-side lower portion, and the door side guide roller unit 87 which can slide on the body side center rail 82 is connected to the rear-side intermediate portion. Moreover, in the slide door 86, a slidable door side lower rail 88 of the body side guide roller unit 83 is installed in the lower portion, and a slidable door side center rail 89 of the body side guide roller unit 83 is installed in the intermediate portion.
Accordingly, the door side guide roller units 87 and 87 slide on the body side lower rail 81 and the body side center rail 82 respectively, the body side guide roller units 83 and 83 slide on the door side lower rail 88 and the door side center rail 89 respectively, and thus, the slide door 86 opens and closes the door opening 80a. That is, in Reference 1, the body side upper rail which is installed along the upper edge of the door opening 80a or the door side guide roller unit which slides on the body side upper rail is eliminated, and thereby, application to the so-called slide door 86 without a door sash (door frame) can be realized.
In addition, as shown in FIG. 6, in a slide door device for a vehicle disclosed in JP 2008-49946A (Reference 2), a hinge 91 is installed on the rear end lower portion of a door opening 90a which is formed on the side of a vehicle body 90, and a body side center rail 92 is installed in a rear quarter panel 90b of the door opening 90a. 
Moreover, a slide door (not shown) is inclined with respect to a front-rear direction due to the hinge 91 while sliding the door side guide roller unit on the body side center rail 92, and opens and closes the door opening 90a. Accordingly, also in Reference 2, the body side upper rail which is installed along the upper edge of the door opening 90a or the door side guide roller unit which slides on the body side upper rail is eliminated, and thus, application to a so-called sedan rear door can be realized.
Moreover, a slide door device for a vehicle disclosed in JP 2009-114782A (Reference 3) is similar to that of Reference 2.
However, in Reference 1, since the door side lower rail 88 and the door side center rail 89 are exposed to a vehicle interior, the design and structure of the slide door 86 (for example, door trim) are limited.
On the other hand, in References 2 and 3, since the hinge 91 is used for the opening and closing of the slide door, an opening-closing amount (door stroke) of the slide door is limited, and thus, the hinge cannot be applied to a slide door which needs a large opening-closing amount. Moreover, it is necessary to increase the size of the hinge 91 in order to support the slide door, and to secure a sufficient disposition space for the hinge around the lower portion of the slide door.
A need thus exists for a slide door device for a vehicle which is not susceptible to the drawback mentioned above.